I drove 123 diesels well over 800,000 miles and a 210 diesel about 70,000 miles. In the 123 days most gas cars were still carbureted, so by comparison, the diesels probably lasted at least three times longer than a gas car and probably offered a 30% or better savings in fuel costs.

Since EFI on gas engines, however, those gains in favor of a diesel are much less if not totally eliminated. If you compare a current diesel to a current gas engine, there is indeed an advantage to the diesel. Comparing a 123 diesel to a later model multipoint injection car is a wash and maybe even in favor of the newer gas car. After all you are talking 20 year newer technology.

The gas engine MB's of the 90's were very fuel efficient and very long lived. I went to an 88 300E I purchased in 1998 with 70,000 miles. It now has 320,000 miles and still running strong. On a vacation trip several years ago, it gave me just a fraction over 29 MPG average on the trip with a few steady Interstate legs of the trip topping 30 MPG. It is a manual transmission car which helps fuel mileage.

All that said, when buying ANY used car keep in mind the top three criteria in selection of a used car:

condition
Condition &
CONDITION

Good luck with your decision.